Space-time distribution patterns of shape Erica australis L. subsp

Plant Ecology 137: 1–12, 1998.
© 1998 Kluwer Academic Publishers. Printed in Belgium.
1
Space-time distribution patterns of Erica australis L. subsp. aragonensis
(Willk) after experimental burning, cutting, and ploughing
Leonor Calvo, Reyes Tarrega & Estanislao de Luis
Area de Ecologı́a, Facultad de Biologı́a, Universidad de León. 24071 León, Spain
Received 4 August 1997; accepted in revised form 22 February 1998
Key words: Experimental perturbations, Regeneration, Reproductive traits, Shrubland, Vegetative resprouting
Abstract
The response of Erica australis to experimental burning, cutting and ploughing treatments was studied in two
heathland communities where it was dominant. The treatments represent those most frequently originated by
humans on these heathland communities throughout history. The response of this species in a community where it is
dominant and there is no strong interspecific competition was also compared to that produced by it in a community
where there is competition. It can be observed that the response to burning and cutting treatments is very similar
with very fast spatial occupation in the first few years. From the point of view of time cover values increased in a
pronounced manner during the first few years and this increase was stabilized from the fourth year. However, from
this moment on a greater increase in this species’ maximum height is evident. The response to ploughing is slower
according to recovery mechanism (seedlings). Recovery is comparatively less in the area where there is no strong
competition than in that where it exists between species.
Résumé
Dans deux communautés de bruyère dominées par Erica australis on a étudié la réponse de cette espèce aux
traitements expérimentaux de brûlage, coupe et labour. Ces traitements représentent les actions les plus fréquentes
que l’homme a exercé sur ces communautés de bruyère tout au long de l’histoire. De la même façon, on a fait
la comparaison de la réponse de cette espèce quand elle se trouve dans une communauté dominée principalement
par elle, où elle n’y a pas une forte compétition entre les espèces, avec la réponse quand elle se situe dans une
communauté où plusieurs espèces coexistent. On observe que la réponse aux traitements de brûlage et coupe est
très semblable, en présentant une occupation spatiale très rapide pendant les premières années. Du point de vue
temporel, leurs valeurs de couverture augmentent de façon plus prononcée pendant les premières années, et c’est
à partir de la quatrième année que ce développement se stabilise. Cependant, c’est à partir de ce moment là qu’on
remarque une augmentation plus grande en ce qui concerne la hauteur maximale de cette espèce. La réponse au
traitement de labour est plus lente en relation avec la régénération par semences. L’effet de la compétition se traduit
par une récupération qui suit un mode d’augmentation opposé à la situation originaire. Dans la surface où il n’existe
pas une forte compétition, la récupération est comparativement plus faible que dans la station où il y existait une
compétition entre les espèces.
Mots clés: Maquis, Mécanismes reproductives, Perturbations expérimentales, Régénération, Rejets
Introduction
Shrub communities cover a wide surface area (33%
of total area) in the province of León in the NW of
the Iberian peninsula, according to the Spanish Ministery of Agriculture (1984). Heathland stands out as
the dominant shrub formation (Luis et al. 1989). These
communities reflect the way of life that has charac-
2
terized our civilization throughout history. The first
arboreal formations were subjected intensely to the
actions of humans as time passed (Calvo 1993). Forest fires stand out amongst the most important ones
(Le Houerou 1969; Naveh 1975; Trabaud 1980, 1991;
Casal 1985, 1987; Luis et al. 1989; Clement & Touffet
1990; Calvo 1993) as well as cutting (Naveh 1982;
Cody 1986). Both provoke the appearance of a mosaic
of ecosystems which represents states of degradation
(Di Castri 1981).
Amongst these states of degradation, shrub communities that have a long history of use and treatment
by humans fundamentally based on the application
of fire, cutting and ploughing are included. Fire has
been the most frequently used of the three (Trabaud
& Lepart 1980, 1981; Gimingham et al. 1981; Mallik
& Gimingham 1983; Ariatnoutsou-Faraggitaki 1984;
Casal 1987; Trabaud 1987, 1991; Calvo et al. 1990,
1992; Tárrega et al. 1995; Clemente et al. 1996). It
has significant effects on the plant species composition of the community mainly due to the temporary
destruction of dominant plants. This dominance is not
generally reestablished until some years have passed
and other woody and herbaceous species become established during this period, thus increasing their
importance values (Mallik & Gimingham 1983).
The second type of action is cutting, the products
of which have different purposes: fuel, fertilizers, etc.
(Casal 1985; Calvo et al. 1992). However, this type
of handling does not seem to have a very disturbing
effect either at a biocoenosis or a soil level (Corns &
La Roi 1976; Casal 1985).
The third type of action on shrubland is ploughing it up in order to turn it into agricultural lands, a
common practice in León province during the 1960s.
This mechanism produces a great change in the whole
vegetation community and the soil (Calvo 1993).
This study simulates experimentally the three actions of humans (burning, cutting and ploughing) on
two heathland communities dominated by Erica australis L. subsp. aragonensis (Willk.) P. Count, which
have different species richness. One of them has only
one dominant species (Erica australis) and the other
the same species co-dominant with Erica umbellata,
Artostaphylos uva-ursi, Calluna vulgaris, Halimium
alyssoides and Halimium umbellatum. (Tutin et al.
1964–1980)
The basic aims of this paper is to define the different recovery patterns through time of Erica australis,
dominant in both communities but with different shrub
specific richness, after being experimentally disturbed.
Materials and methods
Two study areas in the north-east of León province
were chosen. One of them, called Cota Isestil (C.I.)
is at a elevation of approximately 1000 m, exposed to
all winds and its UTM coordinates are 30TUN248336.
The second one is called Palacios de Rueda (P.R.), located 5 km south of C.I. and its UTM coordinates are
30TUN243292. It is on a plain approximately 1150 m
of altitude and exposed to all winds.
The communities in both areas are defined
as a variant of the Genistelo tridentatae-Ericetum
aragonensis-Citisetosum laurifolii community with
Erica australis L. subsp. aragonensis (Willk) (Rivas
et al. 1987) as the dominant species.
It is climatologicalli classified as Mediterranean
Area, with a period of summer drought between July
and August (Ministerio de Agricultura 1980).
From the edaphic point of view the soil is classified
as cambisol húmico (Junta de Castilla y León, 1987).
Physico-chemical parameters of the soil of each communities were studied (Table 1) to determine whether
structure values for both indicate reasonable stability,
that is to say, they are not easily erodible (Cecconi
& Polesello 1956). According to the granulometric
analysis both areas are classified as very sandy. Organic material content as well as total nitrogen, Ca2+ ,
K+ , Mg+ is higher in P. R. than in C.I., whilst total
phosphorus and assimilable phosphorus are higher in
C.I. Both areas have acid soils (pH=5.5).
In each zone, a system of four plots, each measuring 100 m2 , with 3 m wide corridor in-betwing,
was established in those areas with the most homogeneous characteristics possible in cover of species
and in height. One of the four plots was kept with its
original structure. The other three were subjected to
experimental treatments of controlled burning of aerial
biomass, cutting or felling at ground level of woody
biomass and ploughing or uprooting of shrubs with the
stump or roots.
The three treatments were carried out in the P.R.
area in July 1985, and the burning and cutting in July
1985, and ploughing in July 1986, in the C.I. area.
In each plot, 100 sampling units measuring 1 m2
were analyzed before and after carrying out the treatments at yearly intervals for the first five years of
secondary succession and in the eighth and ninth years
(uprooted C.I. plot and the rest of the plots, respectively). The percent cover in vertical projection of each
woody species and the herbaceous ones considered
as a whole, as well as the percentage of bare soil,
3
Table 1. Results of physico-chemical analysis of soil
Physical parameters
C. I.
P. R.
Humidity
%
Structure
Sand
Lime
%
Clay
1.70
4.10
43.50
46.45
79.05
74.50
14.30
18.50
4.95
2.90
Chemical parameters
C. I.
P. R.
O.M.
%
C.E.C.
meq/100gr
Nt
%
Ca2+
K+
Mg2+
ppm
Na+
P
ppm
P2 O5
ppm
pH
4.50
7.36
65.00
68.75
0.16
0.29
1.0
1.7
2.0
2.5
0.4
0.9
0.5
0.5
16
8
36.64
18.36
5.5
5.5
C.I.= Cota Isestil Area.
P.R. = Palacios de Rueda Area.
0.M. = Organic Matter.
C.E.C. = Catyon Exchange Capacity.
were evaluated for each sampling unit. From the fourth
year, when the communities begin to show visible differences in maximun heights of the woody species,
these values were noted for the higher plant for each
sampling unit. This paper is only concerned with the
results for Erica australis.
In order to compare the regeneration of this species
an analysis of variance of repeated measurements in
the comparisons of successive samplings of the same
experimental treatment was used. In order to compare
treatments with each other a two way analysis of variance followed by Scheffe’s test (Scheffe 1959) was
performed.
Results
The mean cover and standard deviation of shrub
species in original state were represented in Table 2.
Average cover values of Erica australis are higher in
area C.I. (62–79%) than in P.R. (29–38%). However,
from the spatial point of view the distribution of this
species is similar in both areas. Average maximun
heights were 80 cm in P.R. and 120 cm in C.I. (Calvo
1993).
Recovery after burning
It can be observed that Erica australis began to recover
one year after burning in both areas (Figures 1 and
2) and occupied practically the whole plot spatially.
Vegetative resprouting caused the spatial reoccupy
from the same places in the original situation, with
a similar pattern of cover in the sampling units. In
successive years there is an increase in cover in each
sampling unit. Considering the entire plots, temporally
(Figure 3) the cover increased considerably until the
fourth year with significant differences in this increase
(Table 3). From the fifth year onwards the increase
slowes.
Original cover values were surpassed and the increase stabilized in the P.R area from the fourth year.
From this moment on, no significant differences were
recorded (Table 3). However, the increase in cover in
the C.I. area was pronounced throughout the study period, although it did not surpass the original values.
It showed significant differences throughout the study
period.
Recovery after cutting
Recovery began in the year after cutting (Figures 1
and 2) in both areas. From this moment on, there was
an increase in spatial occupation with the whole plot
covered in the end of the period of time observed.
A quantitative increase in this species cover was also
observed.
Cover increase in the C.I. area is lower than the
increase shown after burning, whilst it is similar after
both treatments in P.R.
Table 4 shows that significant differences exist in
both areas during the study period.
4
Table 2. Mean cover (and standard deviation) of shrub species in original state
Cota Isestiil
Erica australis
Halimium alyssoides
Calluna vulgaris
Thymus zygis
Crataegus monogyna
Lavandula stoechas
Erica umbellata
Herbaceous spp
Burnt plot
X
d
Cut plot
X
d
Ploughed plot
X
d
78.7
0.1
0.2
62.2
0.1
26.9
1.0
73.8
23.2
1.2
0.5
0.2
2.6
3.6
1.6
0.1
0.6
0.5
1.9
2.3
+
8.3
38.3
5.0
43.1
5.8
1.5
25.1
0.9
0.3
+
25.9
11.1
34.9
6.7
4.8
18.1
4.6
1.7
25.3
1.0
1.4
+
Palacios de Rueda
Erica australis
Erica umbellata
Arctostaphylos uva-ursi
Halimium alyssoides
Chamaespartium tridentatum
Calluna vulgaris
Quercus pyrenaica
Halimium umbellatum
Herbaceous spp
31.4
17.6
43.6
3.9
0.5
21.5
3.9
0.2
+
+
24.5
16.2
39.4
7.2
2.5
18.6
7.2
0.8
28.6
38.4
14.6
6.7
1.6
17.8
1.0
0.4
+
19.9
18.2
24.2
6.6
4.3
14.2
5.0
1.8
X = Mean values of cover.
d = Standard deviation.
+ = Mean cover < 1%.
Table 3. Results of comparison using the Scheffe test based on Repeated Measures
Analysis of Variance of mean cover of Erica australis after burning treatment in both
areas
Cota Isestil
Original
1st year
3rd year
4th year
5th year
1st year
3rd year
4th year
5th year
9th year
211.578∗
97.098∗
22.014∗
50.771∗
55.062∗
7.445∗
32.387∗
78.407∗
17.33∗
2.058
12.562∗
121.03∗
39.809∗
12.823∗
4.608∗
43.115∗
6.783∗
15.695∗
2.983∗
68.78∗
18.762∗
2.857∗
68.17∗
18.445∗
0.00135
15.047∗
109.103∗
42,036∗
4.631 ∗
4.791∗
Palacios de Rueda
Original
1st year
3rd year
4th year
5th year
∗ = Significant differences.
5
Figure 1. Spatial-temporal dynamis of cover and frequency of cover of Erica australis in area C.I. originally and after the experimental
treatments
Recovery after ploughing
Recovery is slower after ploughing (Figures 1 and 2).
Recovery was initiated in the second-third year, but
with very low cover values. Due to this poor recuperation data were not taken in area P.R. until the third year
and in C.I. until the fourth year. The original state was
not attained in area P.R. during the nine-year follow-up
(Figure 3), although the increase is very small from the
fifth year and does not show any significant differences
either compared to the original situation or successive
years (Table 5). Recovery is much slower in area C.I.,
although cover attained during the eighth year is very
high. There are significant differences throughout the
study period (Table 5).
Recovery after the three treatments
On comparing the three treatments in both areas (Figures 1-3) the cover values attained by this species
follow an increase pattern contrary to the original situation. The original values in area C.I. were high but
not surpassed during the nine-year study. In area P.R.
the original cover values were small and had already
been surpassed by the fourth year. This is due to the
fact that once interspecific competition is eliminated,
6
Figure 2. Spatial-temporal dynamics of cover and frequency of cover of Erica australis in area P.R. originally and after the experimental
treatments
the dominant species occupies the greatest area during
the first few years of the secondary succession process.
The cover distribution frequency histograms show that
the frequency distribution does not tend to a similar
state to the original after disturbances in C.I. area, but
tends rather towards a more homogeneous one. This is
not so clear in the P.R. area.
In general it can be seen that cover values attained
in the three treatments are similar in area P.R. after
five years with no significant differences (Figure 3,
Table 6). However, in C.I. there are significant differences between cutting and the other two treatments,
with the smallest cover both in the original state as
well as in the last sampling (9 years after burning and
cutting and 8 after ploughing). Although the initial re-
7
Table 4. Results of comparison using the Scheffe test based on Repeated Measures
Analysis of Variance of mean cover of Erica australis after cutting treatment in
both areas
Cota Isestil
Original
1st year
3rd year
4th year
5th year
1st year
3rd year
4th year
5th year
9th year
91.023∗
52.45∗
5.282∗
28.395∗
17.741∗
3.662∗
19.906∗
25.796∗
7.732∗
0.752∗
6.234∗
49.616∗
22.52∗
8.02∗
3.861∗
27.204∗
5.807∗
7.873∗
0.074∗
30.117∗
7.193∗
0.42∗
34.382∗
9.349∗
0.141
2.900∗
47.867∗
16.914∗
2.047
1.113
Palacios de Rueda
Original
1st year
3rd year
4th year
5th year
∗ = Significant differences.
Figure 3. Cover percentage (and standard error) of Erica australis in both areas after treatments
cuperation after ploughing was slower, at the end of
studied period the cover values were higher than in the
other plots in C.I. but not in P.R.
Modifications in average maximun height
The most pronounced increase in height occurs once
the plants have occupied practically all the space they
originally had and this happens from the fourth year
on.
The height attained after burning is greater than
that reached after cutting and uprooting in both areas
(Figure 4). Height increases in area C.I. throughout the
study period shows significant differences between the
three treatments. The heights attained in area P.R. after
burning and cutting show no significant differences.
After ploughing the increase is smaller, although mean
maximum height of Erica australis is very similar in
the three treatments in the ninth year.
As occurred with cover values, the average maximum height values in area P.R. surpassed the original
values in the fourth year after burning, cutting and uprooting. The increase is very pronounced temporally,
with significant differences (Table 7) in maximum
heights after burning and ploughing. The increase after
cutting is smaller after the fifth year and shows no significant differences. Original heights are not reached
in any case in area C.I. There were only significant
differences after the fifth year (Table 7).
8
Table 5. Results of comparison using the Scheffe test based on Repeated Measures
Analysis of Variance of mean cover of Erica australis after ploughing treatment in
both areas
Cota Isestil
Original
4th year
4th year
8th year
112.946∗
7.797∗
61.394∗
1st year
3rd year
4th year
5th year
9th year
51.7∗
29.225∗
3.184∗
5.158∗
24.197∗
9.827∗
0.431
42.694∗
22.56∗
2.608∗
0.196
58.27∗
34.214∗
7.368∗
1.209
Palacios de Rueda
Original
1st year
3rd year
4th year
5th year
∗ = Significant differences.
Figure 4. Mean (and standard error) of maximum heights of Erica australis.
Discussion
Vegetation developement after different disturbances
tends the community to return to an initial stage and
thus the beginning of autosuccession depends on the
nature of recolonization. When seeds are the main
source, the process is often slower than when vegetative regeneration takes place (Forgeard 1990). It is also
obvious that vegetation structure in autosuccession
processes will be more similar to the original when the
recovery mechanism is vegetation resprouting. Keeley
& Zedler (1978) and Malanson (1985) stated that germinative strategy is favoured in unusual disturbance
conditions, i.e., intervals of 40 years, in shrubs on the
Californian coast after fires whilst vegetative resprout-
ing is favoured by shorter intervals of 20 years. In the
heathland studied, the frequency with which they have
suffered fires is relatively high. However, it can be
observed that species with both reproductive traits coexist, though vegetative resprouting is favoured more
(Calvo 1993).
Both mechanisms are favoured in the dominant
species of these heathlands, Erica australis. Germination is greatly stimulated by fire as it causes
the mechanical breaking of the seed cover, inactivation of inhibitors present in the soil or activation of
the phytochrome system (Ariatnoutsou-Faraggitakki
1984; Keeley & Parker 1990; Menges & Kohfeldt
1995). Vegetative resprouting is also favoured as it
keeps the roots intact and has the capacity to benefit
9
Table 6. Results of comparison using two way ANOVA with repeated measures of mean cover of
Erica australis in the three treatments (comparison using the Scheffe test)
Cota Isestil
Two ways ANOVA of repeated measurement
Source
df
Sum of squares
Treatments (A)
Subjects W. groups
Repeated measured (B)
(AB)
Bx subjects W. groups
2
297
2
4
594
34849.309
384719.957
138856.242
9268.164
195385.593
F-test
P value
13.453
1.0 × 10−4
211.071
7.044
1.0 × 10−4
1.0 × 10−4
Results of application of Scheffe-test
Burnt-Cut
Burnt-Ploughed
Cut-Ploughed
Original
5th year1
9th year1
10.891∗
1.042
5.196∗
8.405∗
7.868∗
0.008
7.158∗
0.238
10.004∗
1 4th and 8th for ploughed plot.
Palacios de rueda
Two ways ANOVA of repeated measurement
Source
df
Sum of squares
Treatments (A)
Subjects W. groups
Repeated measured (B)
(AB)
Bx subjects W. groups
2
295
5
10
1475
1571.51
502196.88
349551.124
15268.698
375113.345
F-test
0.462
P value
0.6307
274.897
6.004
1.0 × 10−4
1.0 × 10−4
Results of application of Scheffe-test
Burnt-Cut
Burnt-Ploughed
Cut-Ploughed
Original
3rd year
4th year
5th year
9th year
0.352
2.281
4.426
0.142
8.936∗
6.826∗
0.435
1.523
3.586∗
0.038
0.042
0.017
0.712
0.0505
0.674
rapidly from nutrients incorporated in the soil after the
first rains. In this way this species, as many other Ericaceae, uses vegetative resprouting as its main recovery mechanism (Mallik & Gimingham 1983; Calvo
1993; Menges & Kohfeldt 1995). Valbuena (1995)
only found resprouts and not seedlings in the post-fire
recovery in a similar Erica australis heathland. Keeley
(1987) stated that the seeds of some species, like Ericaceae, need more than two years to germinate and this
must occur under favourable conditions. Because of
this recovery is basically attributable to vegetative resprouting (Malanson & O’Leary 1982; Oustric 1984;
Forgeard 1990). This allows a fast spatial and quantitative recovery during the first few years; however,
10
Table 7. Results of comparison using the Scheffe test based on ANOVA of repeated
measures of mean maximum heights after the three treatments in both areas
Burnt plot
Palacios de Rueda
4th year
5th year
9th year
3.523∗
2.011∗
Cut plot
Palacios de Rueda
4th year
5th year
9th year
5th year
6.142∗
15.554∗
7.327∗
5th year
1.787
Ploughed plot
Palacios de Rueda
4th year
5th year
8.629∗
52.153∗
18.354∗
5th year
9th year
Cota Isestil
4th year
5th year
9th year
Cota Isestil
4th year
5th year
9th year
1.08
16.51∗
8.945∗
5th year
9.145∗
Cota Isestil
4th year
8th year
the increase in height will be more pronounced than in
cover after the fifth year.
The cutting mechanism, whose effect on biocoenosis is limited to destruction of the aerial biomass of the
shrub but without altering the base and root portions
guarantees the survival of Erica australis as vegetative resprouting is the main recovery mechanism. The
role this mechanism plays in seeds seems to be nil as
germination conditions are not modified in any important way neither as far as nutrient supply nor the
possibility of altering the state of seeds present in the
bank are concerned (Casal 1985). However, this mechanism causes an increase in the amount of light that
reaches the lower parts of the ground and this, together
with the elimination of competition, allows recovery
of herbaceous species present in the area, as Lotus
corniculatus, Aira caryophyllea, Avenula marginata
. . . (Calvo, 1993).
The behaviour of this species after both treatments,
burning and cutting, is similar, due to the fact that
it uses vegetative regeneration as the main recovery
process.
However, it is important to emphasize that the
cover values attained after burning and cutting follow an increase pattern opposite to the original one.
0.782
4.437∗
5th year
139.41
Recovery is comparatively lower in area C.I., where
there was no strong interspecific competition than in
P.R. Erica australis is a shrub species living in frequently disturbed habitats with degraded soils, which
can resprout rapidly and take advantage on other
shrub species as Calluna vulgaris and Erica umbellata, which usually can not resprout in these areas.
These species employed mainly germinative response,
and they reduced their cover after disturbances (Calvo
1993). Thus, on eliminating the competition Erica
australis surpassed the initial values from the fourth
year.
From the edaphic point of view this difference in
recovery can be justified by slight variations in chemical parameters in the soil (Table 1). That is to say,
the area (P.R.) has higher organic matter values, which
means a slight increase in total nitrogen and certain
cations Ca+ , K+ and Mg+2 and greater humidity in
the soil. These slight differences can favour faster
recovery in this species.
An increase in maximum height is observed once
spatial occupation has occurred and cover increase has
been stabilized after cutting in the same way as after
burning.
11
On analyzing ploughing the response is much
slower than to the other two. In this case the only
recovery mechanism that these species can use is seed
germination using either seeds present in the bank or
those from nearby areas that have not been disturbed.
This means that the time needed to begin regeneration
is longer, although the situation is similar to that of the
other treatments from the fourth year on in area P.R.
However, the values are close to initial ones in area
C.I. after eight years.
To summarize, it can be specified that Erica australis, which uses vegetative resprouting as its main
recovery mechanism, occupies all the available surface
spatially one year after burning and cutting. However,
interspecific competition influences the capacity to attain and, in some cases, to surpass initial cover values.
Once the increase in cover has stabilized a significant
increase in height is observed. Ploughing results in
recovery beginning more slowly as the only recovery mechanism is germination. Nevertheless, after the
fourth-fifth year the situation is similar to the original
one as far as cover percentage is concerned.
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